Optimal placement of a casing shoe in a challenging HP environment in the Santos Basin, Brazil: demonstrating the value of lookahead VSP methodology

This paper describes a look-ahead VSP operation that took place in the BM-S-52 concession (Block S-M- 508), Santos Basin, offshore Brazil in June 2009. S-M-508 is a deepwater block located on the north-western edge of the Santos Basin pre-salt province, offshore Brazil, which was awarded to partner Petrobras and BG during the 7th licensing round of 2005 (Figure 1). This paper does not address the numerous recent pre-salt Santos Basin discoveries, nor the geological results from the BM-S-52 drilling campaign. For further detail regarding the pre-salt discoveries, the interested reader is directed to the list of references at the end of this article (Carminatti et al., 2008; Gomes et al., 2008; Moreira et al., 2007). The stratigraphy in S-M-508 comprises (oldest to young­est), a locally untested, at the time of drilling, Aptian-Barremian (and older) pre-salt section, followed by an Aptian evapor­itic interval, overlain by a thick post-salt section, comprising Santonian to Recent clastics. The thickness of the post-salt overburden varies greatly across the block due to irregular salt distribution, and ranges between c. 300 m and 5000 m. Two wells, 6-BG-006P-SPS/Corcovado-1 and 4-BG-007-SPS/ Corcovado-2, were drilled in 2009 during the 1st exploration phase of BM-S-52 between January 2006 and 2010. These wells were drilled in water depths of 818 m and 647 m respectively using the Transocean Celtic Sea rig. The pre-salt section had not been drilled in S-M-508 prior to Corcovado-1 and -2 although the prospectivity in the post-salt interval had been tested by wells 1-BSS-74, -75 and -76 which were drilled in 1994. These wells were located using 2D seismic control and targeted Late Cretaceous, post-salt sandstones.